Khalid al-Falih had opposed Saudi Crown Prince Mohammed bin Salman for months. The powerful energy minister had repeatedly stalled Saudi Aramco’s massive share sale. At a July gathering, he again urged the prince and his advisers to wait before launching what could be the world’s biggest initial public offering. Mr. Falih’s naysaying prompted the prince to call him “the cynical man” and compare him to a slow-moving oil tanker. When Mr. Falih left the meeting room, advisers told the crown prince that he had to go, according…